Pneumatic flapper-nozzle controller



Dec. 15, 1959 w. D. HUSTON 2,917,063

PNEUMATIC FLOPPER-NOZZLE CONTROLLER Filed March 1, 1954 2 Sheets-Sheet 1 I 1%41 INVENIOR MAL/AM fl f/usrarv Dec. 15, 1959 w. D. HUSTON PNEUMATIC FLOPPER-NOZZLE CONTRQLLER 2 Sheets-Sheat 2 Filed March 1, 1954 "J 66' Ovazzu:

INVENTOR Mum/w Q VS 70 ATTORNEYS I A/UZZLE GPE/VM/G) ave/15s United States Patent v 1 2,917,063 PNEUMATIC FLAPPER-NOZZLE CONTROLLER William D. Huston, Sellersville, Pa., assignor to American Machine & Metals, Inc., New York, N.Y., a corporation of Delaware Application March 1, 1954, Serial No. 413,319 1 Claim. (Cl. 137-sz This invention relates to instruments for controlling or indicating purposes and particularly to the flapper and.

nozzle arrangement of a pneumatically operated mechanism.

Pneumatic or air pressure operated controllers or transmitters having a valve or flapper movable relative to a nozzle, the nozzle being connected to a source of air pressure through a restriction, are conventional. The flapper and nozzle thereof are moved relative to each other by a variable condition or operating means. Prior devices have been arranged so that the air blast is substantially at right angles to the flapper face. The nozzle or back pressure can be connected to a pressure relay or pilot which controls air pressure to be transmitted or can be transmitted to a remote instrument, the output pressure of the relay being proportional to the measured variable or the measured condition. A follow-up or feedback means responsive to the output or nozzle pressure can be connected to the nozzle or flapper so as to tend to return the flapper and nozzle to their original relative positions before the change took place.

Difficulty has been found in previous instruments because of a discontinuity in the force relationship required to move the flapper relative to the nozzle, particularly at their most sensitive operating position. This problem arises especially as the nozzle and flapper move relative to each other when closely spaced from each other, such as when within about .002 apart with a nozzle of 0.020" diameter. There is a force reversal" effect involved which causes serious disturbances or unstable conditions. Force reversal effect may be defined as the condition existent when the nozzle and flapper are moved from open positions wherein the force necessary to move them relative to each other is substantially constant until a point is reached where the force suddenly. decreases to a minimum and then rapidly increases until the flapper and nozzle are completely closed. It is obvious that such will result in undesirable unstable conditions.

One of the objects of the present invention is to provide a nozzle and flapper arrangement which will have a nozzle or flapper moving force relationship substantially.

rangement which will reduce the amount of force required to move the flapper and nozzle together as the nozzle approaches its force reversal position for flapper and nozzle combinations of equal capacity and similar characteristics.

In one aspect of the invention, the flapper and nozzle can be moved relative to each other by any suitable mechanism, such as for example the unitary. algebraic comparing means illustrated in copending application, Serial No. 391,049 filed November 9, 1953, now Patent No. 2,785,696. In such an arrangement, an expandible element responsive to changes in a measured variable can be connected to an algebraic comparing means which is also the output or nozzle back pressure. In one form, the flapper can be moved relative to the nozzle by the comparing means output. The nozzle has a supply of air connected thereto through a suitable restriction. In accordance with the particular invention herein, the nozz le is arranged relative to its baflle so that the axis of the 2,917,061? Patented Dec. 15, 1959 other than relative to the flapper face. Of course, the

angle must be greater than 0". Preferably, the angle of the axis of the air blast relative to the baffle when the nozzle and baflle are substantially closed relative to each other, should be between 30 and 65 with respect to a perpendicular to the baffle face juxtapositioned to the nozzle. The term substantially closed means when the nozzle and baffle are spaced no more than 10% of the internal diameter of the passage in the nozzle adjacent its face. As will be explained hereafter, location of these parts and surfaces angularly relative to each other will give decidedly improved operating characteristics.

These and other objects, advantages and features of the invention will become apparent from the following description and drawings.

In the drawings:

Fig. 1 is a front elevation of the pertinent parts of one form of instrument with which the invention can be used, air feed pipes and some other parts being shown schematically;

Fig. 2 is a graph showing movement and nozzle pressure relationships;

Fig. 3 is an example of an instrument assembly containing the invention, some portions being illustrated schematically.

As previously mentioned, the invention. will be described in conjunction with an instrument having a unitary algebraic comparing means for moving the flapper and nozzle relative to each other. It is to be understood, however, that other types of instruments may be employed for carrying out relative movement of the flapper and nozzle. As schematically illustrated in Figs. 1 and 3, the air supply is indicated at 10 and is fed through a restriction means 11 to pipe 12 which has one portion 13 leading to the air inlet opening 14 of the nozzle assembly 41. .Pipe 15 may be connected to device 16, device 16 being a recorder, air relay or other mechanism operable in response to the change of air pressure in the nozzle. Feed line 17 is connected to the interior of the output pressure element 25. Input element 20 may take the form of a capsule assembly as shown or may be a bellows or any other type of responsive or positioning mechanism including a bi-metallic arrangement or suitable movable means. to the interior of capsule 20 is illustrated at 18.

the instrument.

ing mechanism. Segment 27 is operable by link 26 which is movable by the output pressure responsive means 25,, segment 27 being mounted on shaft 27A held in the frame of the instrument. Segment 27 operates the secondi pinion 28 of the dilferential mechanism according to: movement of output pressure capsule 25, pinions 29 and. 30 cooperating with the input pinions of the differential mechanism 24. The differential mechanism 24 is sup ported on shaft 32 suitably carried by the frame of the machine.

The output of the differential mechanism is transmitted to the segment plate 31 which has gear teeth 31A therein The measuring device connected Supply airis admitted to the nozzle 41 through passage'M in the body 48 of the nozzle, the body dfi'being' suitably adjustablysupported on the instrument frame.

Normally retracted cleaning element or plunger 46 may bemanually moved by handle or knob 47 so as to enter passage 42 and remove any dirt therefrom. Spring 44 serves to hold the cleaning plungen ifi in a retracted position as illustrated in Fig. 1.

Because of the air'stream or blast issuing from the V nozzle passage 42, force must be exerted on flapper" 34 in theform shown-in order to move the parts together in response to a change in the variable. The force required for such movement will be a function of the back pressure in the nozzle. 7

When the nozzle is arranged relative to the flapper so that the axis of the air blast is substantially perpendicular to the flapper face, there will be disturbances and unstable conditions existent as the nozzle approaches close to the flapper in the effective operating range. When the nozzle and flapper are relatively close, which is true of the normal operative range, the disturbances and unstable conditions have been the source of much difficulty and inaccuracies. relationshipbetween the back pressure in the nozzle and the distance of the flapper from the mean center ofithc nozzle passage is illustrated. Curve A thereof shows the back pressure vs. distance relationship in the conventional nozzle arrangement where the air blast axis is at right.

angles to the flapper. 'It is to be noted that as thenozzle reaches a position approximately 0.00 from the flapper, there is a sudden reduction in back pressure which will lower the force required at this point to move the parts relative to each other and this will result in an extremely unstable condition. The exact reason for such a force reversal or reduction in pressure is not entirely certain. Furthermore, the back pressure before the force reversal point is reached is higher with the nozzle having. its axis perpendicular to the flapper than is the case with nozzles arranged in accordance with the inventioneherein. The nozzle in the particular graph shown was one having an internal diameter of 0.020" and the supply pressureused was 18 lbs. per sq. in.

When the axis of the air blast or jet is inclined 30 relative to the perpendicular to the flapper face, it is'seen in curve B that the back pressure when the parts'are' separated more than .002" is less than in the case of the nozzle having an axis perpendicular to the flapper. Furthermore, the force reversal effect or reduction in pressure as the parts approach each other is substantially eliminated or reduced 'so not seriously to affect operation as compared with the perpendicular axis nozzle. When the nozzle is so inclined so that its axis is 45 relative to the perpendicular to the flapper face, the force reversal effect or force discontinuity is further attenuated as can be seen in curve C. Then as the angle of the nozzle blast axis relative to the perpendicular to the flapper face is increased to 65, the force reversal effect isstill Within.

satisfactory limits and substantially"eliminated.as comparedwith the nozzle perpendicular tothe flapper face,

such being illustrated in curve D. Further. increase in the angle will result in a discontinuity which becomes serious and introduces unstable and undesirable conditions. Although not definitely established, some of this may be due to effect of the increasedface area at the nozzleas its face becomes elongated. Thus, the angle of the axis of the air blast relativeto the perpendicular in Fig. 2, an example. of the 4 to the flapper face when the nozzle and flapper are substantially closed preferably should be in the range of 30 to 65 It can be theorized, although it is to be understood that this is not entirely certain, that in the case of a nozzle perpendicular to the flapper face when-they are close to each other, the forces involved are affectedby the increased velocity of air flowing radially from the nozzle because of closeness of the parts and that such causes a pressure drop which lessens the force required to hold the flapper. In contrast, when the parts are angled as described herein, then the velocity relationship is effective against a smaller area of the nozzle face because the air is being directed in onedirection,

and not'radially in all directions.

In addition to stability of'operation, angular arrange-" ment of the nozzle will tend to keep the faces of the= flapper and nozzle clean. When at right angles, in some instances a cup shaped globule of oil or foreign matter may form between the nozzle andflapper seriously af fecting the force relationships and aetuations. As the angle is'increased, it may be desirable to reduce'wall thickness of the nozzle adjacent the opening so as to eliminate possibility of errors being introduced because of' air friction.v

A. lighter net'force is' required to operatethe parts whenother than substantially closed and this is of importance because of sensitivity required in an instrument of the typei'nvolved herein.

It normally would be expected that the relationship offorceto hold the flapper vs. distance of the flapper relative to' thenozzle would smoothly continuously in crease as theparts approach each'other, but as can be seen in Fig. 2, such is not the case. tially constant straight line relationship followed bya decreaseand then a rapid increaseas the parts approach each other.

Details of construction and arrangement can be made without departing front the spirit of the invention except as defined in the appended claim.

What is. claimed is:

In a condition responsive apparatus for producing an output pressure in response to a measured variable, the

combination including a nozzle having a bore there'- through connected to a source of fluid pressure through a restriction, saidnozzle having a face sloped relative'to the axis ofsaid bore, a flapper having a flat face which cooperates with said sloped face to control fluid flow" fromv saidxbore, said flat face of said flapper and saidsloped face of said nozzle being movable relative to each" other by changes in the measured variable, measured variable responsive means, means connecting said bore to said responsive means, mounting means holding the axis of said bore at an angle of between 30 and 65" relative: to the perpendicular to said'fiat face of the flapper so. that the axis of the air blast from the bore willbeat an. angle relative to said perpendicular to said face at least when the nozzle is spaced a distance-within 10% of the internal diameter of the bore adjacent the sloped face of the nozzle.

References Cited in the file of this patent V UNITED STATES PATENTS There is a substan--- 

